1. Field of the Invention
This invention relates generally to an apparatus for separating according to size a quantity of particulate material that contains various sizes of particles, and more particularly relates to an apparatus with at least one moving screen that separates particulate material according to size by the particulate falling through the screen or screens.
2. Description of the Related Art
Moving screens are used to sort material by size in various industries including mining, construction, waste disposal, landscaping and demolition. Some screens are substantially planar and vibrate at least partially in a direction transverse to the plane of the screen. Material placed on the screen vibrates with the screen and the particles that are smaller than the openings in the screen fall through and collect beneath the screen or are conveyed to a location spaced from the screen, such as by a chute and/or conveyor belt.
Other screens are not planar but are cylindrical, and these screens are called barrel or “trommel” screens. Barrel screens have at least one screen that is cylindrically shaped to form a cage-like screening structure. The barrel screen's longitudinal axis is angled relative to horizontal during use, and the barrel screen is rotated about its longitudinal axis. The material to be processed is placed in the open mouth of the higher end and the rotation and the angled axis cause the material to tumble toward the lower end with smaller, screened material falling down through the apertures of the screen. The material that does not pass through the screen is discharged out of the open mouth of the lower end. The screened material can accumulate on the ground below the barrel screen or can fall onto a conveyor belt or chute that is positioned to catch the material and convey it out from beneath the screen. Likewise, the material that passes out of the lower end of the barrel screen can fall on the ground or be conveyed away on a chute or conveyor belt.
A typical barrel screen apparatus has a barrel screen with a length that is greater than its diameter, and a conveyor belt that is aligned lengthwise beneath the barrel. The lengthwise conveyor extends out the front or the rear of the apparatus, or a lateral conveyor receives the material from the lengthwise conveyor and conveys it laterally at any position intermediate the two ends of the apparatus or at one of the two ends. Other barrel screen apparatuses have different barrels and permit the screened material to fall onto the ground below the barrel.
Portable barrel screening machines are known in the prior art. Conventional portable barrel screening machines have an input conveyor, a rotary barrel screen and a longitudinal conveyor beneath the barrel screen, all of which are mounted together on frame. The frame is provided with wheels at one end and a “fifth wheel” at the opposite, for connection to a conventional semi-tractor vehicle or is mounted on tracks. Other conventional barrel screening machines have a planar screen followed by a first conveyor that receives the material that passes through the planar screen, a barrel screen that receives the material from the first conveyor and a second conveyor that receives the material that falls through the barrel screen and conveys it away from the barrel.
The material that is to be screened by conventional machines is typically fed into the receiving end of a barrel screen by a conveyor belt, onto which material is dumped. The material that is first poured onto the conveyor is not always processed prior to entering the barrel screen. If the material is processed before entering the barrel screen, it is processed by a large planar screen or a hammermill, followed by a conveyor that conveys the pre-screened material into the barrel screen as described above.
The prior art configurations have the disadvantage that the length required for the apparatus is large. If the material is not pre-processed, the barrel screen must be very long to sufficiently screen the charge of particulate. Alternatively, if the material is pre-processed by a planar screen or a hammermill, the entire apparatus is especially long due to the second conveyor's length. These long machines cannot be transported easily over the road. Therefore, the need exists for a screening machine that is effective, but can be transported easily.